This invention pertains to an ink set for inkjet printing, in particular to a non-aqueous ink set comprising one or more inks based on certain pigment colorants. The invention also pertains to a method of inkjet printing with this ink set.
Inkjet printing is a non-impact printing process in which droplets of ink are deposited on print media, such as paper or polymeric substrates, to form the desired image. The droplets are ejected from a printhead in response to electrical signals generated by a microprocessor.
Ink can comprise colorant that is dissolved (dye) or dispersed (pigment) in the ink vehicle. The ink vehicle can be aqueous or non-aqueous and the ink is referred to as aqueous or non-aqueous ink, accordingly.
Aqueous ink is advantageous because water is especially environmentally friendly. There are many applications though where aqueous ink is unsuitable and non-aqueous ink must be used. Many if not most of these non-aqueous ink applications involve printed articles, and particularly printed articles on polymer substrates, which will be exposed to sunlight and the preferred colorants are pigments because of their well-know advantage in fade resistance compared to dyes.
Dispersion of pigment in non-aqueous vehicle is substantially different than dispersion in aqueous vehicle. Generally, pigments that can be dispersed well in water do not disperse well in non-aqueous solvent, and vice versa. Also, the demands of inkjet printing are quite rigorous and the standards of dispersion quality are high. Thus, pigments that may be “well dispersed” for other applications are often still inadequately dispersed for inkjet applications.
There is a need for improved pigment selection for non-aqueous inkjet inks. In particular, there is a need for pigments in non-aqueous ink that provide improved chroma and transparency, while still retaining good resistance to light fade and appropriate hue angle.